Willem Bruin (born 1759 at de Rijp, died 22 October 1826 at Westzaan) was pastor of the Mennonite church at Kolhorn, Wieringen, and Westzaan (op het Noord), all in the Dutch province of North Holland. He was one of the lay preachers who distinguished themselves by unusual capability in the ministry and in writing. Deprived of his parents in early childhood, and entirely without means, he grew up in the orphanage of his home town de Rijp in North Holland. In spite of his extraordinary talents, evident in his schoolwork, he was taught the carpenter's and mill-builder's trade, in which he did competent work. In his youth he applied himself to religious studies, stimulated by de Groot's book, Over de Waarheid van den christlijken Godsdienst (On the Truth of the Christian Religion). At the age of 22 he was baptized.

His pastor P. Hartman recognized his great gifts and his interest in religious questions, and suggested that he become a preacher. But there was no fund to finance his training; so Bruin devoted all his spare time to studying alone and with his pastor. After six months he preached his first sermon in the vacant pulpit of the church at Kolhorn and Barsingerhorn (1783) and was called to serve there as preacher after passing an examination conducted by the preachers Jan ten Kate and Sybrand Martens and being declared capable of the service. In 1784 he became a minister on the island of Wieringen and in 1786 in Westzaan, where he served with great blessing over 40 years (1786-1826).